Many radiotelephones are powered by a battery. Those battery powered radiotelephones that minimize power consumption and conserve battery power have a commercial advantage as they help extend the battery operating time.
The radio communication system in which radiotelephones operate include a plurality of channels. The radiotelephone employs a receiver to repeatedly scan among the plurality of channels while the radiotelephone is not in service. The receiver scans through the plurality of channels until it finds one containing service quality data. It is known to periodically power off the receiver during channel scanning to conserve battery power. Known intermittent receiver operation schemes that save battery power during channel scanning are shown in the timing diagrams of FIGS. 1 and 2.
FIG. 1 shows a receiver that is initially powered on to perform a continuous scan of all the channels (23 through 43 and 323 through 343) for a predetermined time period, such as 60 seconds. If no channel with service quality data is found during the 60 seconds, the receiver goes into an intermittent scan mode to save battery power. During the intermittent scan mode the receiver is periodically powered on for a scanning period during which data on the strongest channels is examined. The receiver is powered off for a second predetermined time period, such as 9 seconds, between each scanning period. The intermittent scan mode is interrupted when the user actuates a key on a keypad of the radiotelephone or when service quality data is found on a channel during the scanning period.
However, the scheme of FIG. 1 will only save battery power if no service quality data is found during the continuous scan and then only by powering off the receiver for the second predetermined time period during the intermittent scan mode. No battery power is saved during the continuous scan or during the scanning periods of the intermittent scan mode. Additionally, there is no opportunity for the radiotelephone to find service quality data when the receiver is powered off during the second predetermined time period.
In FIG. 2, a receiver scans all of the channels (1 through 40) during a period T. One channel is scanned during each time period t.sub.1. The receiver is powered on for a first portion of t.sub.1 (denoted by a solid line) during which data on the channel is examined and powered off for a second portion of t.sub.1 (denoted by a dotted line). The receiver cycles through each channel until all of the channels are examined for service quality data. The scanning cycle is continued until a scanned channel is determined to contain service quality data.
However, because the scheme of FIG. 2 must determine if service quality data is present at the time each channel is scanned, the scanning period T and partial scanning time t.sub.1 must be lengthy. Also, the scheme of FIG. 2 does not discern between weaker and stronger channels having service quality data, but instead selects the first channel with service quality data.
Therefore, what is needed is a channel scanning apparatus and method without lengthy continuous scanning periods, without lengthy periods where the receiver is powered off, and without service quality data checks during the scanning of each channel.